1. Field of the Invention
This invention relates to purification of scandium and more specifically, this invention relates to the isolation and purification of medical radioisotopes from irradiated targets.
2. Background of the Invention
Radioisotopes play important roles in numerous areas ranging from medical treatments to national security and basic research. Some examples include investigations of structures and reactions involving atomic nuclei, Mossbauer spectroscopy, radio-thermoelectric generation and other nuclear batteries, nuclear device detection, nuclear non-proliferation, cancer diagnosis and therapies.
Radionuclide production technology for medical applications has been pursued since the early 1900s both commercially and in nuclear science centers. The ionizing nature of the emissions of certain radioactive isotopes can be used to destroy malignant biological tissues. The unpredictable and fast-acting properties of tumors and infectious diseases demand that radionuclide therapies employ a wide arsenal of radioisotopes of differing radioactive emissions. Many medical radioisotopes are now in routine production and are used in day-to-day medical procedures, with production centers currently seeking FDA approval for additional radioisotopes. Despite these advancements, research is accelerating around the world to improve the existing production methodologies as well as to develop novel radionuclides for new medical applications.
For more than 40 years, the National Nuclear Security Administration (NNSA) has targeted the conversion of world-wide research reactors from highly-enriched uranium (HEU) to low-enriched uranium. This is problematic inasmuch as these HEU reactors are a pivotal source of medical radioisotopes such that the conversion of these reactors may curtail isotope availability. Although high specific activity (HSA) radioisotopes are important in nearly all aspects of radiochemical work, most radionuclides produced in nuclear reactors have low specific activity due to the inherently limited production reaction pathways, (n,γ) that only change the mass number and not the atomic number and thus not the identity of the element. Specific activity refers to the radioactivity of a given radioisotope per unit mass, usually per mass of the ground state of the element of interest present in the sample.
In order to achieve HSA radioisotopes, the product of nuclear reactions must be chemically different and separable from the target material. These are the keys to producing HSA radioisotopes. In the medical sense, HSA radioisotopes are essential for radioisotope therapy or radioimmunotherapies (RIT). Here HSA radioisotopes are bound to specific sites that are coordinated to targeting vectors that seek markers expressed on/in cancer tissues. Low specific activity radioisotopes will not work for these applications as the nonradioactive target material (or non-useful isotope) will compete for the binding site meant for the radioisotope. Fewer agents with the desired cancer fighting payload (radioisotope) make it to the cancer site, thus decreasing the effectiveness of the therapy.
Separation of desired radioisotope from the target material is of paramount importance for medical applications as well as for radiological source preparation, and nuclear fuel reprocessing. Technologies described herein for the chemical separation of radioisotopes from target materials can also be useful for industrial applications such as the isolation of pure products from ores and mineral deposits and visa versa.
Radionuclides with ionizing beta emissions, several day half-lives, and appropriate gamma emissions are potential candidates for radioimmunotherapy. Scandium-47 is an emerging combined therapeutic and diagnostic (theragnostic) medical isotope that can be used for targeted radionuclide therapies in the treatment of a variety of tumors and rheumatoid arthritis. Sc-47 is a β emitter of moderate radiation energies (max. 439 and 600 keV) with a 3.35 day half-life. In addition, Sc-47 emits a γ-ray of 159 keV, which is suitable for Single Photon Emission Computed Tomography (SPECT).
Methods researched for the production of high-specific activity Sc-47 include nuclear activation of enriched titanium targets by fast-neutron reactors, high-energy proton accelerators, or electron accelerators. Carrier free (HSA) Sc-47 can be produced in a nuclear reaction either from Ti-47 (n,p) or from Ca-46 (n,γ).
State of the art scandium isolation and purification protocols require complex and time-consuming separation avenues. Lengthy steps with columns and metal complexing agents are often required. Multiple solvent extraction steps using multiple ion exchange columns are employed in state of the art methods.
Also, these processes are long, in excess of 8-12 hours. These long processing times are particularly troublesome inasmuch as the desired radio-isotope is decaying with time and therefore lost over extending processing times.
Given these shortcomings in scandium isolation and purification protocols, the availability of scandium is potentially very expensive and uncertain. Therefore, while Sc-47 has very desirable half-life of 3.35 days, the medical community is forced to use less viable alternatives.
A need exists in the art for a system and method for economically isolating and purifying Sc-47. The system and method should integrate several element harvesting procedures in as few steps as possible and omit excessively hazardous or complex reagents so as to render product as quickly as possible. Furthermore, the system and method should eliminate or at least minimize secondary waste streams, and provide the option of recycling the target material.